Feared and expected, the emerald ash borer has been found in Minnesota, posing a critical threat to the state's 900 million ash trees, including roughly one-third of all trees in Minneapolis and St. Paul.

The infestation was discovered in a tree on Long Avenue in St. Paul's Hampden Park neighborhood. State officials got a preliminary confirmation from a federal entomologist who viewed a digital picture Thursday. They are expecting final confirmation today from a sample sent to Washington.

"It's pretty clear this is the emerald ash borer, and it's the first discovered in the state," said Minnesota Department of Agriculture spokesman Mike Schommer. "It's obviously bad news."

Minnesota has the second highest number of ash trees in the nation after Maine. Many of them were planted to replace trees lost to Dutch elm disease a generation ago, when streets in countless neighborhoods lost their shade.

The discovery is expected to halt movement of any ash brush, limbs, stock or other parts into or out of Ramsey and Hennepin counties beginning today. A similar quarantine is in place in Houston County, in the state's southeast corner, for only three weeks, after the insects were found about 20 miles east in Wisconsin last month.

Since its accidental introduction into North America -- no one knows when -- the emerald ash borer has killed millions of ash trees in 10 Eastern states. In Michigan, the bug wasn't identified until 2002, because it wasn't even known to live in the United States, although it may have been chewing its way through ash trees for more than a decade. More than 20 million trees have been lost there.

Geir Friisoe, director of plant protection for the state Department of Agriculture, said Minnesota may be in a better position to fight the tiny metallic-green beetle, which is native to China and Korea.

"Certainly we're going to lose a lot of ash, both in the urban forest and in the wild," Friisoe said. "We're going to take a pretty major hit, but it's not going to be a complete loss."

Friisoe said research into natural predators in China, including a stingless wasp, could lead to biological controls. Meanwhile, trees with slight infestations of bugs sometimes can be successfully treated.

What to look for

For now, residents should first identify ash trees, which have fine-textured bark and stems surrounded by five to 11 leaves. Trees with upper branches that are dying, or are sprouting "suckers" along the trunks, or are showing woodpecker damage, are probably infected. D-shaped holes in the bark are also evidence of the emerald ash borer larvae escaping.

Tree care experts will remove patches of bark from suspect trees to look for tell-tale squiggly insect paths. If the tree is not entirely circled by the insect paths, it is a candidate for treatment, though that can be costly. Otherwise its condition is terminal, because the insects will have cut off the flow of nutrients between the tree's leaves and roots.

Experts believe that ash borers, thought to have been brought to the United States in packing crates from China, have been moving far faster than they naturally would by people transporting firewood and through other common means of travel.

A year ago, they had been detected only as far west as Chicago and eastern Wisconsin. But last month they turned up in southwestern Wisconsin, near La Crosse.

"We'd hoped this day would be delayed two years or more," said Bob Fitch, executive director of the Minnesota Nursery and Landscape Association. "But honestly, I'm not surprised that it's here."

Fitch noted that the insect has already been affecting Minnesota's tree population for seven years.

Nurseries stopped producing ash shortly after the borer was discovered in the United States in 2002, and few have been sold or planted since, effectively knocking out what had been a healthy market.

The ash borer infestation in St. Paul was discovered by a commercial arborist who had been examining trees around an apartment complex on Long Avenue.

Friisoe said it appears that all the trees on the street will have to be removed.

He added that residents and public arborists should take care not to plant just one species of tree to replace lost ash. That strategy, following the Dutch elm plague, was a "mistake," he said.

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